1. Field of the Invention
The present invention relates to a display device, and more particularly, to a color filter substrate and a method of fabricating the same that prevent brightness failure from at an edge a liquid crystal display (LCD) device.
2. Discussion of the Related Art
As the modern society changes into an information-oriented society, an LCD display device has been in the limelight. Cathode ray tubes (CRTs), which are widely used up to now, have many advantages in aspects of performance and price, but they also have many disadvantages in aspects of miniaturization and portability. On the contrary, LCD devices have advantages of miniaturization, lightweight, slim profile, and low power consumption, and are drawing attention as an alternative capable of overcoming the disadvantages of the CRTs.
FIG. 1 is a partial schematic view of an LCD device according to the related art. In FIG. 1, an LCD device includes a color filter substrate 22, a thin film transistor (TFT) substrate 21, and a liquid crystal layer 17. The color filter substrate 22 includes a first insulation substrate 20, a black matrix 13 formed of chromium (Cr) or resin on the first insulation substrate 20, and a color filter layer 15 having red (R), green (G) and blue (B) color filter elements formed between lattices of the black matrix 13. In addition, a common electrode 11 of a transparent conductive metal is disposed on the entire surface of the first insulation substrate 20 including the black matrix 13 and the color filter layer 15. Further, the TFT substrate 21 facing the color filter substrate 22 includes a plurality of gate lines 1 and a plurality of data lines 3 intersecting the plurality of gate lines 1 to define a unit pixel region, a thin film transistor (TFT) 5 that is a switching element, and a pixel electrode 9 on a second insulation substrate 10.
The LCD device having the above construction controls light transmittance by rotating liquid crystal molecules of the liquid crystal layer 17 using an electric field generated between the pixel electrode 9 and the common electrode 11. Such light then passes through the R, G and B color filter layer 15 to display a color image.
FIG. 2 is a plan view of a color filter substrate of an LCD device according to the related art, and FIG. 3 is a cross-sectional view along I-I′ of FIG. 2. In FIG. 2, a color filter substrate includes a black matrix 31 having a lattice structure on a substrate 30. R, G and B color resins are disposed between the lattices of the black matrix 31 to form red (R), green (G) and blue (B) color filter layers 35a, 35b and 35c. The black matrix 31 is formed in the shape of a lattice, and red (R), green (G) and blue (B) color filter layers 35a, 35b and 35c are disposed between the lattices of the black matrix 31. The R, G and B color filter layers 35a, 35b and 35c have the same thickness.
However, the color filter substrate having the above construction has a brightness failure at an edge region. For example, the edge region is much brighter than other regions. The brightness failure may be due to one or more of the following various reasons. First, pixel electrodes of the TFT substrate corresponding to an edge region of a color filter layer have fewer adjacent pixel electrodes than the pixel electrodes of other regions, e.g., pixel electrodes of a center region. As such, an electric field generated by the pixel electrodes disposed along the edge region is different from an electric field generated by the pixel electrodes disposed on a region other than the edge region, thereby causing brightness failure. Such a brightness failure can occur at all four edge regions of a panel, such as the upper edge region, the lower edge region, the right-side edge region and the left-side region.
In addition, a brightness failure can be caused by an alignment failure in an alignment layer, which is on the TFT substrate or the color filter substrate. For example, a rubbing process establishes an intended alignment direction in the alignment layer. However, the rubbing process can fail to establish the intended alignment direction at an edge portion of the alignment layer due to a height difference at the edge portion. As such, liquid crystal molecules at such an edge region are not aligned in the same manner as liquid crystal molecules at other regions. Thus, non-uniform brightness can occur at all four edge regions of a panel, such as the upper edge region, the lower edge region, the right-side edge region and the left-side region.
Further, in a storage-on-gate type LCD device, a dummy gate line overlaps pixel electrodes formed along the 1st gate line of the TFT substrate, and a predetermined value of gate low voltage Vgl is applied to the dummy gate line to form a storage capacitance in the pixel electrodes corresponding to the 1st gate line. However, for the pixel electrodes corresponding to gate lines other than the 1st gate line, a storage capacitance is generated between a (N−1)th gate line to which a pulse voltage is applied, and a pixel electrode corresponding to an Nth gate line. Thus, the storage capacitance of the pixel electrodes corresponding to the 1st gate line is different from the storage capacitance of other pixel electrodes, thereby causing brightness non-uniformity at an upper edge region.
Moreover, the 1st data line and the last data line have an asymmetric structure not having an adjacent pixel electrode, unlike other data lines. In particular, Cdp values generated between the 1st data line and the pixel electrodes corresponding to the 1st data line and between the last data line and the pixel electrodes corresponding to the last data line are different from Cdp values between other data lines and pixel electrodes corresponding to the other data lines. Since the Cdp values affect the storage capacitance formed in each pixel electrode, a brightness failure occurs at the lateral edge portions, i.e., the 1st data line region and the last data line region.